1. Field of the Invention
The present invention relates to output devices, and more particularly to output devices that use toner to produce an image. Still more particularly, the present invention relates to a method and system for variable toner output in output devices.
2. Description of the Prior Art
Several types of output devices use toner as the means for producing images, such as text and graphics, on a page. Examples of such output devices include laser printers, copiers, and facsimile machines. Typically, the cost of toner is a significant expense when operating these types of output devices. For example, paper can cost approximately one cent per page while toner can cost one to ten cents a page depending on the amount of toner used.
Contemporary output devices, such as printers, have an economy output mode in addition to a normal output mode. When selected, the economy output mode reduces the amount of toner used on a page during printing. Economy output mode is useful when a lower quality print is desired, such as when printing a draft of a document or checking the layout of a page.
One drawback to contemporary economy output mode implementations is that many are implemented using a low resolution screen to mask a fixed percentage of all picture elements, or pixels. In other words, pixels are printed by dropping out a certain percentage of pixels in some fixed pattern regardless of the image content. The problem with this is that at times a user can detect transitions, or defects, in the image after it is produced. This is especially true if the transition occurs on a edge of a character or graphic. This is because the human perception system is more sensitive to edges than to smooth transitions.
FIGS. 1(a)-1(c) depict a prior art system for variable toner output in an output device. FIG. 1(a) illustrates the original image, which in this example is the word "Test". A fifty percent fixed mask is used as the economy mode in the output device, as shown in FIG. 1(b). When the word "Test" is produced using the economy mode, pixels are printed by dropping out a certain percentage of pixels (i.e., 50%). The resulting image is illustrated in FIG. 1(c). As can be seen, transitions between filled pixels and non-filled pixels occur inside each letter as well as on their edges. Because the human perception system is more sensitive to transitions on the edge of an image, a user may detect defects (i.e., the transitions) in the image when produced using this prior art system.
Another drawback to contemporary economy output mode implementations is that the toner is typically reduced by a fixed amount, such as fifty percent. A user can not select the amount of toner reduction. For example, a user may desire a larger toner reduction, such as seventy-five percent when producing draft documents. Alternatively, a user may want to reduce toner output by only twenty percent. With current economy output modes, a user can not select the amount of toner reduction, but must instead employ the amount of toner reduction that has been predetermined by a manufacturer.